The present invention relates generally to an apparatus for sealing a web of film. More specifically, the present invention relates to an apparatus for sealing a web of film in a form, fill, seal packaging machine.
Typically, form, fill, seal packaging machines are utilized to package a product in a flexible container. To this end, form, fill, seal packaging machines are used to seal pharmaceuticals, dairy products, wine, food stuffs, cosmetics, and other products in flexible containers. The form, fill, seal packaging machine provides an apparatus for packaging these products in an expedient manner.
In one type of form, fill, seal packaging machine, a web of heat-sealable film is passed over a former or mandrel that forms the film into a tubular shape. To effect the tubular shape, the film is folded longitudinally and heat-sealed along abutting longitudinal edges. The tubular-shaped film is then passed around a tubular fill system that deposits the product to be packaged into the tubular-shaped film. To create individual packages (hereinafter "bags"), the web of film must be sealed across its width to form side seals. These side seals are usually created by a sealer that creates the second seal for one bag while making the first seal for the next bag. Typically, after the side seals are created, the web of film can then be severed between the seals to create individual bags.
There are a variety of different methods for sealing the web of film to create a seal in the web of film. One method is to utilize a sealing member. In a typical form, fill, seal packaging machine, the sealing member is secured to a set of jaws that are hydraulically actuated to grip the web of film. For example, in creating the side seals, as the jaws grip the web of film, the sealing member is urged against the film welding a portion of the web of film onto itself. Typically, after the hot bar has melted the web of film, a knife is actuated and severs the web of film between the seals to create a flexible bag.
In creating, specifically, the side seals in a web of film, one of the problems inherent therein is heating the web of film to a sufficient temperature so that it is melted and sealed onto itself and cooling same before the packaging machine is cycled to the next step in the process, so that the seals do not come apart or weaken. In a typical form, fill, seal production packaging machine, the cycle time of the machine is approximately 3 seconds. Accordingly, during this 3-second period, the jaws must come together, the web of film must be melted, and then the web of film must be cooled sufficiently so that the film can be advanced to the next stage of the process.
Some of the previous form, fill, seal packaging machines have not sufficiently cooled the web of film during the cycle time and accordingly, resultant bags created by these machines have had an unacceptable number of seal failures. One of the difficulties in cooling the sealing member or bar is that typically, it is covered or coated by a release layer such as a Teflon tape. This release layer prevents film from sticking to the sealing member, but, also makes it difficult to sufficiently cool the sealing member.
The failure to cool the film sufficiently fast typically results in two types of defects. One defect is that the molten material is drawn into a fibrous form resulting in a weaker seal. A second defect is that under internal pressure, the molten seal upon opening the jaw can separate resulting in leaks and/or a weak seal.
In certain industries, the strength of the seals is more critical than in others. For example, in the pharmaceutical industry, flexible bags for housing parenteral or enteral products are typically subjected to drop tests to test their strength. One test that is sometimes utilized is a six foot drop test. Obviously, if the seals are not strong, the flexible bag will not survive a six foot drop.
Another disadvantage with some of the prior form, fill, seal packaging machines is that the web of film is not sufficiently heated or is heated to too great of temperature during the sealing process. Of course, if the web of film is not sufficiently heated, there will not be a sufficient interfacial mixing of the molecules of the film and accordingly, a strong seal will not be created. If the film is heated to too great of temperature, there is a danger that the film will stick to the surface of the sealing member. There is also a danger of film degradation if the film is heated to too great a temperature.
Controlling the temperature to which the film is heated is difficult. In sealing the film there are certain processing uncertainties that have made it difficult to heat the web of film to a specific temperature. These process variables include: powerline fluctuations to the heater; heater resistance change over time; heater resistance change with respect to ambient temperatures; ambient temperature and humidity change; the effect of the filling medium on the heat transfer from the sealing member to the film; power transmission conversion equipment accuracy; power contact resistance changes; and uncertainties and inconsistencies due to the release layer. Furthermore, the release layer must be changed every 6-8 hours due to its degradation.
Although a number of these variables could be eliminated and the remaining ones controlled, if it were possible to measure the temperature on the film, heretofore, it has been difficult to measure the temperature of the web of film as it is being heated. One of the difficulties stems from the fact that the sealing member, which heats the web of film, is either coated with a release layer to prevent the web of film from sticking to the sealing bar, or includes a protective covering, such as a Teflon tape. Thus, it is not possible to measure the temperature of the film and regulate the sealing bar accordingly, because the sealing bar does not directly contact the web of film.
Accordingly, there is a need for an improved apparatus for sealing a web of film in a packaging machine.